Quick reset induction time delay device



June 25, 1957 R. E. CORDRAY QUICK RESET INDUCTION TIME DELAY DEVICE Filed April 25, 1953 x y an P 5/? m nfi A 3f 11H .lm/v m QUICK RESET INDUCTEGN TIME DELAY DEVICE Richard E. Cordray, Nether Providence Township, Pa., assignor to General Electric Company, a corporation of New York Application April 23, 1953, Serial No. 350,584

7 Claims. (Cl. 317-66) The invention relates to induction time delay devices, particularly overcurrent relays of the inductive type having very inverse time delay characteristics.

The principal object is to provide such an electroresponsive induction relay or the like with an improved electromagnetic induction drag energization control combination for selectively introducing a desired long time delay in the operation of a movable induction element as well as eliminating the electromagnetic drag to enable a quick reset of the element to be obtained.

Ordinarily the time delay in the operation of the movable induction element of a relay is obtained by interlinking a permanent magnet so as to produce eddy current braking action or drag upon movement of the induction element in both the operating and the reset directions. Thus, the reset time delay of such induction relay inherently is about the same as the operating time delay. This is often quite undesirable particularly where a very long time delay relay operating characteristic is required.

Also when a very long time delay in the operation of a relay induction element is desired, the increased magnetic braking action or drag requires the use of a very high strength permanent magnet of the Alnico type.

Thus another object of the present invention is to provide an induction drag electromagnet control combination that can be used as a substitute for a high strength permanent magnet in very long time delay electro-responsive induction relay service with the added advantage of quick reset.

Another object is to maintain the drag electromagnet deenergized under normal conditions and energize the drag electromagnet only when the magnetic drag is required.

In carrying out the invention in a preferred form the rotatable induction element of a time delay overcurrent relay is spring biased to the reset position and is provided with a drag electromaguet for producing a very strong non-directional magnetic drag to retard the rotation of the element. An instantaneous overcurrent responsive relay preferably having its operating winding energized in series with the operating winding of the time delay overcurrent relay is provided with contacts for selectively controlling the energization of the drag electromagnet so as to produce the drag only upon operative energization of the series connected windings. In this manner a retarding influence is exerted on the induction element when rotating in its operating direction, while the drag is eliminated and the element is free to quickly reset upon removal of the operative energization of both windings.

Further objects and advantages of the invention will appear in the following description of the accompanying drawing in which the single figure is a schematic perspective view of a time delay overcurrent induction type relay provided with the improved drag electromagnet energization control combination of the present in Vention.

ames Patented June 25, 1957 As shown schematically .in the drawing, the tripping winding it) of the circuit breaker 11 is energized under the control of the time delay responsive overcurrent induction relay indicated generally by the reference character 12. This relay 12 is provided with the improved induction drag electromagnet control combination of the present invention to enable a very inverse tripping characteristic to be obtained as well as to enable a quick reset of the induction relay to be obtained as soon as the circuit breaker 11 opens the circuit.

The induction disk element 15 of relay 12 is axially mounted on the pivot shaft 16 that is supported in suitable bearings not shown. Shaft 16 is biased to rotate in the clockwise or reset direction by the spiral spring 17 until the contact operating arm 18 engages with the adjustable stop 19. The driving electromagnet 21 for the induction disk element 15 produces a driving torque in the counterclockwise or forward direction when its magnetizing winding 22 is energized in response to predetermined overcurrent conditions in the circuit conductors L1, L2, L3 by means of suitable current transformers 23. The operating winding 25 of an instantaneous responsive overcurrent relay 26 is shown connected in series with the magnetizing winding 22 so as to enable relay 26 to respond instantaneously to the same overcurrent conditions as the time delay overcurrent relay 12.

The driving electromagnet 21 is provided with the usual pole shading windings 2'7 in order to produce the driving torque by inducing eddy currents in the induction disk 15 of sufficient strength to overcome the biasing force of the spiral spring 17 and thereby drive the contact operating arm it; in the counterclockwise direction away from stop 19 whenever the predetermined overcurrent condition occurs in any one or all of the circuit conductors L1, L2, L3.

In accordance with the present invention under such predetermined overcurrent conditions, the drag electromagnet 34 is interlinked with the induction disk 15 so as to induce strong eddy currents therein and thereby create a magnetic braking action that will retard the counterclockwise or forward rotation of the disk 15. Under all normal current conditions the magnetizing winding 35 of the drag electromagnet 34 remains deenergized. But upon the occurrence of the predetermined overcurrent conditions in the protected circuit, the instantaneous overcurrent responsive relay 26 closes its contact and thereby energizes the winding 35 from a suitable supply source indicated as plus and minus so as to produce strong non-directional retarding action during the counterclockwise rotation of the disk 15 by the driving electromagnet 21. As a result, a time interval is introduced into the circuit breaker tripping operation of the induction overcurrent relay 12. The time delay is inversely proportional to the overload current in the circuit protected by the circuit breaker 11. Thus under very slight overload conditions, a very long time delay is introduced while under very heavy overload conditions a very much shorter time delay is introduced before the arm 18 is rotated to engage the contacts 30 and thereby energize the trip coil 10 of the circuit breaker 11 from the supply source plus and minus. This will result in the release of the latch 31 and the opening of the circuit breaker 11 to interrupt the flow of overload current in the circuit conductors L1, L2, L3.

Upon opening of circuit breaker 11 a quick reset of the time delay overcurrent relay 12 is immediately produced. This is due to the fact that upon the opening of circuit breaker 11 both the windings 25 of the instantaneous overcurrent relay 26 and the magnetizing winding 22 of the driving electromagnet 21 are deenergized. The resulting opening of relay 26 deenergizes the magnetizing winding 35 of the drag electromagnet 34. Consequently,

there is no magnetic drag to delay the return rotation of the induction disk 15 in the clockwise direction by the bias of the spiral spring 17. Thus the contacts 30 are quickly opened to deenergize the tripping winding and the arm 18 quickly returns into engagement with the adjustable stop 19.

In this way the improved drag electromagnet energization control combination of the present invention enables the quick reset of the time delay overcurrent induction relay 12 to be obtained. Use of the instantaneous overcurrent relay 26 aids in producing a quick reset after only partial operation of relay 12 even though circuit breaker 11 does not open. Thus, whenever a brief period of excessive overcurrent in the circuit conductors is followed by a reduction of the current to a value below that predetermined amount required to drive induction disk 15 forward, relay 26 Will open to deenergize magnetizing winding 35 thereby eliminating retarding action while disk 15, which has rotated through a portion of its total travel due to the excessive overcurrent, quickly returns to its fully reset position.

While I have shown and described a preferred form of my invention by way of illustration, many modifications will occur to those skilled in the art. I therefore contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a movable induction element having means for biasing the element to a reset position, current responsive means for moving the element forward from the reset position when the current exceeds a predetermined value, a drag electromagnet interlinked with the induction element for retarding movement thereof upon energization of the electromagnet, and current responsive means for energizing the drag electromagnet only when the current exceeds the predetermined value thereby to retard forward movement of said induction element while enabling said induction element to quickly return to the reset position when the current is interrupted.

2. In combination, a movable induction element having means for biasing the element to a reset position, an electro-responsive driving device inductively interlinked with the induction element for moving the element forward from the reset position upon energization of the electro-responsive driving device in excess of a predetermined amount, a drag electromagnet inductively interlinked with the induction element, and an electro-responsive switching device connected to energize said drag electromagnet in response to excessive energization of the electro-responsive driving device thereby to retard forward movement of said induction element and to produce a quick reset of the induction elementwhenever the energization of said electro-responsive driving device becomes less than the predetermined amount.

3. In combination, a time delay overcurrent induction relay having a rotatable induction element provided with means biasing the element to a reset position and having overcurrent responsive means including a first winding for rotating the element forward from the reset position upon a predetermined energization of the first winding and having electromagnetic drag means including a second winding for retarding the rotation of the element upon energization of the second winding, and an instantaneous overcurrent responsive relay having a third winding energized in series with said first winding and provided with switching means for energizing said second Winding only during the predetermined energization of the first winding to retard only forward rotation of the induction element.

4. In combination, a circuit breaker having tripping means including a movable induction element provided with means biasing the element to a reset position, a first means responsive to the current in the circuit for moving the element forward from the reset position to a tripping position when the current exceeds a predetermined value, a drag electromagnet interlinked with the induction element for retarding forward movement thereof upon energization of the drag electromagnet, and a second current responsive means interconnected with the first current responsive means for energizing the drag electromagnet only when the current exceeds the predetermined value thereby to produce a quick reset of the induction element when the current is reduced below the predetermined value.

5. In combination, a movable induction element having means for biasing the element to a reset position, electro-responsive means for moving said induction element forward from the reset position upon energization of the electro-responsive means in excess of a predetermined value, a non-directional retarding electromagnet interlinked with said induction element for retarding movement thereof upon energization of the electromagnet, and means for energizing said retarding electromagnet during excessive energization of said electroresponsive means and deenergizing said retarding electromagnet in response to the reduction of the energization of said electro-responsive means below said predetermined value thereby eliminating the effect of said retarding electromagnet on said induction element to permit a quick reset thereof.

6. In combination, a movable induction element biased to a reset position, electro-responsive means for moving said element forward from its reset position when energized in excess of a predetermined amount, a drag electromagnet energizable to retard movement of said element, and means responsive to less than said predetermined amount of energization for maintaining said drag electromagnet deenergized.

7. An overcurrent relay for initiating tripping operation of an electric circuit breaker comprising, a movable induction element biased to a reset position, current responsive means effective when energized in response to circuit current having greater than a predetermined mag nitude to move said element forward from its reset position to a tripping position, an electromagnet coupled to said element to retard movement thereof when energized,

and means energizing said electromagnet only when said current responsive means is effective to move said element forward.

References Cited in the file of this patent UNITED STATES PATENTS 1,027,440 Schley May 28, 1912 2,619,522 Glassburn Nov. 25, 1952 FOREIGN PATENTS I 337,119 Great Britain Oct. 30, 1930 

